The present invention relates to an electrophotographic image processing apparatus for forming a latent image on a photosensitive body by scanning a laser beam, and forming an image by developing this latent image with toner.
In conventional digital copying machines, particularly monochromatic digital copying machines (DPPCs), the tone reproduction characteristic is caused to saturate in a high-density portion. Therefore, the stability in this high-density portion with respect to environmental variations is not an important problem in image quality.
Also, to improve stable reproducibility in a low-density portion, a gray level processing system has been proposed by which halftone processing methods for a low-density portion are switched. However, no invention has improved stable reproducibility in a high-density portion.
In color image recording apparatuses such as color digital copying machines, the tone reproduction characteristic is desirably linear. Additionally, stable reproducibility highly resistant to environmental variations is required even in a high-density portion, since unstable tone reproduction leads to variations in hue. In electrophotographic recording in which a latent image is formed on a photosensitive body by scanning a laser beam and developed with toner to form an image, to improve the reproducibility in a high-density portion it is necessary to reduce unstable intermediate transition regions, which exist in the boundaries between image portions and non-image portions, and in which toner is either developed or not developed.
A non-image portion is a region in which no toner image is formed because the region is not exposed, or not satisfactorily exposed, to a laser beam. In pulse width modulation type laser driving, a pulse OFF state exists in one pixel, and this portion is a non-image portion.
It is an object of the present invention to detect a high-density portion and, if a high-density portion is detected, switch to a gray level processing method by which non-image portions of a plurality of pixels are clustered, thereby reducing the area of intermediate transition regions and improving the reproducibility and stability of the pixel structure in this high-density portion.
According to the present invention, there is provided an image forming method comprising the steps of:
reading an image signal in units of pixels;
generating a first driving signal corresponding to an image portion and a non-image portion in one pixel based on the read image signal of each pixel;
generating a second driving signal for clustering non-image portions of a plurality of pixels, on the basis of the read image signal of each pixel and an image signal of a peripheral pixel;
detecting whether the read image signal of each pixel has a density not less than a predetermined density;
selectively outputting the first driving signal if the image signal of the detected pixel has a density not less than the predetermined density;
selectively outputting the second driving signal if the image signal of the detected pixel has a density not more than the predetermined density;
outputting a laser beam on the basis of the selectively output first or second driving signal;
forming a latent image on a photosensitive body with the laser beam; and
forming an image by developing the formed latent image with toner.
According to the present invention, there is further an image forming apparatus comprising:
reading means for reading an image signal in units of pixels;
first generating means for generating a first driving signal corresponding to an image portion and a non-image portion in one pixel based on the image signal of each pixel read by the reading means;
second generating means for generating a second driving signal for clustering non-image portions of a plurality of pixels on the basis of the image signal of each pixel read by the reading means and an image signal of a peripheral pixel;
detecting means for detecting whether the image signal of each pixel read by the reading means has a density not less than a predetermined density;
first output means for selectively outputting the first driving signal generated by the first generating means if the image signal of the pixel detected by the detecting means has a density not less than the predetermined density, and selectively outputting the second driving signal generated by the second generating means if the image signal of the pixel detected by the detecting means has a density not more than the predetermined density;
second output means for outputting a laser beam on the basis of the first or second driving signal selectively output by the first output means;
forming means for forming a latent image on a photosensitive body with the output laser beam from the second output means; and
developing means for forming an image by developing with toner the latent image formed by the forming means.
According to the present invention, there is still further an image processing apparatus comprising:
detecting means for detecting whether a density of an image signal of an input pixel is not less than a predetermined density;
first converting means for converting the image signal into image signals of an image portion and a non-image portion for each pixel on the basis of the density of the image signal of each input pixel and a pixel position of each input pixel;
second converting means for converting the image signal into image signals of an image portion and a non-image portion for each pixel, on the basis of the density of the image signal of each input pixel and the pixel position of each input pixel, thereby clustering image signals of non-image portions of a plurality of pixels; and
output means for selectively outputting the image signal from the second converting means if the detecting means detects that the density of the image signal of the input pixel is not less than the predetermined density, and selectively outputting the image signal from the first converting means if the detecting means detects that the density of the image signal of the input pixel is not more than the predetermined density.
According to the present invention, there is still further an image processing apparatus comprising:
detecting means for detecting whether a density of an image signal of an input pixel is not less than a predetermined density;
first storage means for storing first basic dither information of a dither matrix used to cluster non-image portions of a plurality of pixels;
second storage means for storing second basic dither information of a dither matrix used to cluster image portions of a plurality of pixels;
first output means for selecting the first basic dither information stored in the first storage means if the density of the image signal of the pixel detected by the detecting means is not less than the predetermined density, selecting the second basic dither information stored in the second storage means if the density of the image signal of the pixel detected by the detecting means is not more than the predetermined density, and outputting dither information, based on the first or second basic dither information selected and a pixel position of the input pixel, as a threshold value;
second output means for quantizing the image signal of the input pixel by the threshold value from the first output means and outputting the quantized image signal;
first generating means for generating coordinate information in a main scan direction and coordinate information in a sub-scan direction based on the pixel position of the input pixel;
second generating means for generating a reference position signal in the pixel from the coordinate information in the main scan direction and the coordinate information in the sub-scan direction generated by the first generating means;
third output means for outputting an image density signal of a pixel to be processed after pixel value shifting, from the coordinate information in the main scan direction and the coordinate information in the sub-scan direction generated by the first generating means and the image density signal quantized by the second output means; and
fourth output means for outputting as the reference position signal in the pixel generated by the second generating means and the image density signal of the pixel to be processed after pixel value shifting output from the third output means.
According to the present invention, there is still further an image processing apparatus comprising:
a plurality of converting means for converting each input pixel of a two-dimensional image in a main scan direction and a sub-scan direction into an image density signal;
a plurality of generating means provided in one-to-one correspondence with the plurality of converting means to generate a driving signal on the basis of the image density signal from a corresponding converting means; and
output means for selecting the driving signal from one of the generating means at each main scan period of each input pixel of the image, and periodically changing a main-scan-direction initial phase, selected whenever scan is performed, in the sub-scan direction and outputting the phase,
wherein the converting means include converting means for converting an input pixel corresponding to a high-density portion into an image density signal in a saturated range and converting means for converting an input pixel corresponding to a high-density portion into an image density signal in an unsaturated range.
According to the present invention, there is still further an image processing apparatus comprising:
a plurality of converting means for converting each input pixel of a two-dimensional image in a main scan direction and a sub-scan direction into an image density signal;
a plurality of generating means provided in one-to-one correspondence with the plurality of converting means to generate a driving signal on the basis of the image density signal from a corresponding converting means; and
output means for selecting the driving signal from one of the generating means at each main scan period of each input pixel of the image, and periodically changing a main-scan-direction initial phase, selected whenever scan is performed, in the sub-scan direction and outputting the phase,
wherein the converting means include converting means for converting an input pixel corresponding to a high-density portion into an image density signal in a saturated range, converting means for converting an input pixel corresponding to a high-density portion into an image density signal in an unsaturated range, converting means for converting an input pixel corresponding to a low-density portion into zero or an image density signal in a range within which no image is formed, and converting means for converting an input pixel corresponding to a low-density portion into an image density signal in a range within which an image is formed.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed-out hereinafter.